FIG. 1 illustrates a sheet 3 of material, such as plywood or gypsum wallboard. Such a sheet 3 is generally installed over framing members 6, which can take the form of joists, studs, or rafters. One installation method utilizes an electric drill, which drives threaded screws through the sheet, and into the framing members 6.
However, when a screw is to be installed a distance from the edge 9 of the sheet, such as at point 12 along central longitudinal axis CAX, it is difficult to locate the framing member 6, because that member is not visible at point 12. One solution to the problem is to visually estimate the position of the framing member 6, but that approach often results in errors, and produces screws which must be removed because they miss the framing member 6.
Another solution is to snap a chalk line across the sheet 3, which is aligned with the visible parts of the framing member 6, as from points P1 to P2. This solution is effective, but time-consuming.